The invention relates to an access control device for a motor vehicle in which access to the motor vehicle is permitted only when authorization is demonstrated. The invention also relates to a method for setting the sensitivity of the access control device.
An access control device which is known from German Published, Non-Prosecuted Patent Application DE 36 27 193 A1 has a transmitting and receiving unit in the vehicle. As required, the transmitting and receiving unit transmits a request signal and then waits for a reply signal from a portable encoder (question-answer dialog). If the reply signal is received, it is compared with an expected signal in an evaluation unit. If the two signals correspond, door locks are unlocked or an immobilizer is released.
In that case, the request signal is transmitted from an antenna in a side mirror when the user actuates a switch on the door handle. However, it is possible in that case for the encoder, which the user carries with him or her, to be too far away from the exterior mirror, with the result that the encoder does not receive the request signal. That is the case particularly when the user carries the encoder in a pocket on the side remote from the side mirror.
It is accordingly an object of the invention to provide an access control device for a motor vehicle and a method for setting the sensitivity of an access control device, which overcome the hereinafore-mentioned disadvantages of the heretofore-known devices and methods of this general type, in which the access control device rapidly identifies a user""s desire for access and reliably carries out a question-answer dialog, and in which the method ensures that interference signals only slightly affect the question-answer dialog or not at all.
With the foregoing and other objects in view there is provided, in accordance with the invention, in a motor vehicle having at least one door with a door surface, at least one door handle, and at least one locking unit, an access control device for the motor vehicle, comprising a transmitting and receiving unit disposed at the vehicle for transmitting a request signal and for receiving a reply signal; an evaluation unit in the transmitting and receiving unit for comparing the reply signal with an expected code signal and for controlling the at least one locking unit in dependence on a result of the comparison; a portable encoder for receiving the request signal, for returning a coded reply signal, and for demonstrating authorization of or enabling a user carrying the encoder to lock and unlock at least one locking unit; and a transmitting and receiving antenna connected to the transmitting and receiving unit, the antenna having cores and at least two coils each wound onto a respective-one of the cores, the coils disposed in at least one door handle at a distance from the door and at an inclination relative to the door surface.
In this case, the access control device has a transmitting and receiving antenna formed from a plurality of individual coils. The coils are approximately cylindrical and are disposed in the door handle with their axes inclined at an angle with respect to one another. This has the advantage of producing a widely fanned radiation characteristic of the antenna, depending on the installed position of the coils. As a result, the encoder which is situated in the vicinity reliably receives the request signal that is transmitted with the aid of the magnetic field.
In accordance with another feature of the invention, there is provided a switch disposed on or in the door handle or in proximity to the door handle. Through the use of this switch, the user can trigger the question-answer dialog in a simple manner by actuating the door handle. The request signal is transmitted to the encoder in that dialog.
In accordance with a further feature of the invention, a plurality of coils are disposed in each of the door handles of both the front and rear doors and then if the encoder is situated outside the motor vehicle in the region of the rear doors, it is also addressed.
In accordance with an added feature of the invention, the individual coils are driven electrically differently in terms of amplitude and phase, so that differently resulting magnetic fields are produced. Consequently, the radiation characteristic of the antenna can be altered if the encoder does not receive the request signal even though it is close enough to the motor vehicle.
In accordance with an additional feature of the invention, the coils are disposed along the door handle in such a way that their axes are disposed at an obtuse angle with respect to one another. This gives rise to a magnetic field extending away from the motor vehicle (with a great depth).
In accordance with yet another feature of the invention, a plurality of coils are disposed with each of their axes perpendicular to the door handle. This gives rise to a widely fanned magnetic field.
With the objects of the invention in view, there is also provided a method for setting the sensitivity of an access control device, which comprises increasing a reception sensitivity of the portable encoder if a request signal can be expected and the encoder previously received an advance signal for that purpose with increased transmission power from the transmitting and receiving unit at the motor vehicle; and reducing the reception sensitivity of the encoder a period of time after transmission of a reply signal or after reception of a special signal.
In accordance with a concomitant mode of the invention, there is provided a method which comprises transmitting the advance signal with a considerably increased transmission power in comparison with the subsequent request signal.
The sensitivity of the access control device is set by the request signal being preceded by an advance signal having a considerably increased transmission power. If the advance signal is identified by the encoder, then the reception sensitivity of the encoder is increased for a period of time.
Consequently, further request signals with small levels are also received. Interference signals, which are constantly present at a certain level, in this case have no effect or only little effect. on the process of the question-answer dialog, as long as the levels of the interference signals are smaller than the reception level. It is advantageous for the subsequent request signal to be transmitted with a lower transmission power, so that energy is saved during transmission. Likewise, components are disburdened or relieved due to a smaller current load. A high continuous load endurance capacity is not required, thereby enabling all of the components to be configured to be smaller and simpler. The electrical voltages across components can be rated lower, which means that a risk to the user of electric shock is ruled out.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an access control device for a motor vehicle and a method for setting the sensitivity of an access control device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.